Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 379 - AVS Forum
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Audio Theory, Setup, and Chat > Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs
jim19611961's Avatar jim19611961 11:45 AM 09-02-2014
Quote:
Originally Posted by jkasanic View Post
^^^I believe you meant UMM-6 USB mic above
I just called Parts Express to find out. The mic that comes with the Omnimic kit is neither the UMM-6 or the EMM-6. This is the mic I use. They say its exclusive for that kit.

jkasanic's Avatar jkasanic 11:52 AM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
I just called Parts Express to find out. The mic that comes with the Omnimic kit is neither the UMM-6 or the EMM-6. This is the mic I use. They say its exclusive for that kit.
Yeah, I knew you were using the OM kit mic (more similar to a UMM-6 than the EMM-6 because it's USB) so I was more responding to the fact that the EMM-6 is not a USB mic. HST, until now I wasn't sure if the OM mic was really any different to the UMM-6 since I've owned both and there's no discernible difference in appearance.
jim19611961's Avatar jim19611961 11:55 AM 09-02-2014
Quote:
Originally Posted by jkasanic View Post
Yeah, I knew you were using the OM kit mic (more similar to a UMM-6 than the EMM-6 because it's USB) so I was more responding to the fact that the EMM-6 is not a USB mic. HST, until now I wasn't sure if the OM mic was really any different to the UMM-6 since I've owned both and there's no discernible difference in appearance.
Was their any discernible difference in the measurement data they provided?

Additionally, PE said there was "extra stuff" in the OM version. They added it may not work right with anything other than OM. Made my day
jkasanic's Avatar jkasanic 12:06 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
Was their any discernible difference in the measurement data they provided?

Additionally, PE said there was "extra stuff" in the OM version. They added it may not work right with anything other than OM. Made my day
Several months ago (heck, maybe even over a year now?!), there was a discussion in this thread around the use of the UMM-6 with OM as well as the OM mic with REW. To my knowledge, the latter has been reported but not the former. The physical appearance of the mic is identical as well as the case and accessories. I sent my OM kit back when I realized how much more robust/versatile REW was so I never had the chance to swap mics and compare the data. I also believe at that time that OM didn't support the cal file from CSL (or perhaps I have it mixed up and REW didn't support the cal file from OM) so that was a limiting factor but I believe that is no longer the case.

I haven't been following this latest issue in detail but from the posts I've read, all signs point to the use of a USB mic (UMM-6, UMIK-1 or the OM version) and no loopback as the major variables. How that relates to how REW retrieves and displays the data is beyond me.
Bluescale's Avatar Bluescale 12:11 PM 09-02-2014
Quote:
Originally Posted by jkasanic View Post
I haven't been following this latest issue in detail but from the posts I've read, all signs point to the use of a USB mic (UMM-6, UMIK-1 or the OM version) and no loopback as the major variables. How that relates to how REW retrieves and displays the data is beyond me.
I don't think loopback is an issue, because Markus tried it with and without loopback, and the data was the same.
jim19611961's Avatar jim19611961 12:12 PM 09-02-2014
Quote:
Originally Posted by Bluescale View Post
I don't think loopback is an issue, because Markus tried it with and without loopback, and the data was the same.
Good point. But not with a USB mic. Or was it?
Bluescale's Avatar Bluescale 12:16 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
Good point. But not with a USB mic. Or was it?
No, he didn't have a USB mic. Is it even possible to do the loopback connection with a USB mic?
jkasanic's Avatar jkasanic 12:18 PM 09-02-2014
Quote:
Originally Posted by Bluescale View Post
I don't think loopback is an issue, because Markus tried it with and without loopback, and the data was the same.
Yeah, I forgot Markus reported no issue with and without the timing reference loopback so good point indeed. Could be another anomaly with the USB mics (like the spikes issue and higher noise floor).
jkasanic's Avatar jkasanic 12:19 PM 09-02-2014
Quote:
Originally Posted by Bluescale View Post
No, he didn't have a USB mic. Is it even possible to do the loopback connection with a USB mic?
AFAIUI, no it's not possible.
jim19611961's Avatar jim19611961 12:25 PM 09-02-2014
Quote:
Originally Posted by Bluescale View Post
No, he didn't have a USB mic. Is it even possible to do the loopback connection with a USB mic?
Quote:
Originally Posted by jkasanic View Post
Yeah, I forgot Markus reported no issue with and without the timing reference loopback so good point indeed. Could be another anomaly with the USB mics (like the spikes issue and higher noise floor).
Have either of you performed the test? Result?
3ll3d00d's Avatar 3ll3d00d 12:26 PM 09-02-2014
Quote:
Originally Posted by jkasanic View Post
AFAIUI, no it's not possible.
that's correct

the measurements look like they contain noise before the impulse to me. If you look at the IR on overlay with dBFS scale, zoom in on -2ms to +2ms and see how the level before the impulse increases with each sweep until it blows through the full scale, at that point it loops over itself before the main impulse.

I think the next step is to try and rule out different parts of the signal path; for example going to a short direct USB connection, switching USB cable, switching USB ports and so on.

I don't see how loopback has anything to do with it as that just gives it the system time so it can calculate the flight time correctly. The reported measurement itself doesn't change when you mess around with loopback (e.g. set it so it receives no signal or so you clip the loopback signal).
jim19611961's Avatar jim19611961 12:30 PM 09-02-2014
Quote:
Originally Posted by 3ll3d00d View Post

the measurements look like they contain noise before the impulse to me. If you look at the IR on overlay with dBFS scale, zoom in on -2ms to +2ms and see how the level before the impulse increases with each sweep until it blows through the full scale, at that point it loops over itself before the main impulse.
I agree. It does look that way on the 512k and 1M sweeps. But not on the 256k sweep.

Quote:
Originally Posted by 3ll3d00d View Post
I think the next step is to try and rule out different parts of the signal path; for example going to a short direct USB connection, switching USB cable, switching USB ports and so on.
I tried all three of those things to no avail.

Remember. I tried this whole affair on my laptop and got the same results.

I have also tried it using my PC speaker system with the same results.

When I used my RS SPL meter as the mic, the problem went away.

The only common factor is REW and the mic. They don't like each other it seems. The puzzling thing is Jerry is having the problem also, and he is using a different mic than me.
AustinJerry's Avatar AustinJerry 12:47 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
The puzzling thing is Jerry is having the problem also, and he is using a different mic than me.
Until you pointed it out, I didn't realize I had a problem, Jim. Just think, two years of REW work down the drain. I guess I'll start over now.
jim19611961's Avatar jim19611961 12:51 PM 09-02-2014
Quote:
Originally Posted by AustinJerry View Post
Until you pointed it out, I didn't realize I had a problem, Jim. Just think, two years of REW work down the drain. I guess I'll start over now.
I wouldn't go that far. The 256k sweeps agree very closely with the data obtained by Omnimic. Since OM is a kit, and each part is meant to work with the others, I can only assume OM with the OM mic is pretty accurate. That said, you use 256k most of the time anyway. So while there is a mystery here, if your data is off, I don't think its by much.
3ll3d00d's Avatar 3ll3d00d 12:59 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
I agree. It does look that way on the 512k and 1M sweeps. But not on the 256k sweep.
they all look the same to me, they just burst through the peak level at different times

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This is from -2.5ms to +0.1ms

I've drawn lines to show what I mean (I changed the 512 trace to blue to distinguish it from the other green one)

tbh even the 128 one looks dodgy, I don't see anything like that in any of my traces. They're usually like this

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jkasanic's Avatar jkasanic 01:02 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
Have either of you performed the test? Result?
I have not tried it. If there's no progress on this issue before my next measurements then I'll be sure to try it the next time I have my room setup.
3ll3d00d's Avatar 3ll3d00d 01:04 PM 09-02-2014
Quote:
Originally Posted by AustinJerry View Post
Until you pointed it out, I didn't realize I had a problem, Jim. Just think, two years of REW work down the drain. I guess I'll start over now.
I don't think all (or anything really) is lost. As far as I can see, the etc's look basically the same which is, afaik, what you use it for. If you were doing impulse or phase related work (e.g. XO design) then I think you'd have noticed the problem before now. FWIW the phase view is another one that shows variation btw (though I think some variation is expected when you don't have loopback)

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markus767's Avatar markus767 01:06 PM 09-02-2014
Quote:
Originally Posted by Bluescale View Post
So, I have a question about this. My sub is a Rythmik D15SE, which is downward firing. Downward firing works well in my room because I have concrete floors If I flip it upside down on the couch, so the sub is firing toward the ceiling, it'll be pretty close to ear height.

Does the direction of the driver make a difference? For that reason alone, I haven't bothered to do the sub crawl. I always move it to possible locations, and measure, which is a pain with such a big sub.
Orientation doesn't matter as long as the driver is at ear height.

Easy to check if you're doing it right: Put the mic at some location in the room and measure. Then swap location of mic and sub and re-measure. The result should look more or less the same.
LastButNotLeast's Avatar LastButNotLeast 01:12 PM 09-02-2014
Quote:
Originally Posted by AustinJerry View Post
Until you pointed it out, I didn't realize I had a problem, Jim. Just think, two years of REW work down the drain. I guess I'll start over now.
At least now there's a great guide you can follow.

jim19611961's Avatar jim19611961 01:15 PM 09-02-2014
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Jerry, here is REW vs OM. Same mic location. One right after the other. As you can see, the ETC's look very very similar. And ETC is one of those areas where the file size problem shows the most.
Attached:
jim19611961's Avatar jim19611961 01:25 PM 09-02-2014
Quote:
Originally Posted by 3ll3d00d View Post
they all look the same to me, they just burst through the peak level at different times

Attachment 242466

This is from -2.5ms to +0.1ms

I've drawn lines to show what I mean (I changed the 512 trace to blue to distinguish it from the other green one)

tbh even the 128 one looks dodgy, I don't see anything like that in any of my traces. They're usually like this

Attachment 242474
What I should have said is that the 128k and 256k look "more" normal than the 512k and 1M
3ll3d00d's Avatar 3ll3d00d 01:34 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
What I should have said is that the 128k and 256k look "more" normal than the 512k and 1M
Does omnimic let you change the sweep length? What does the ir look like in omnimic? Same as REW or different.

You, and Jerry, could also try HolmImpulse if you want another data point. This would help isolate either the app or the mic/signal chain.
jim19611961's Avatar jim19611961 01:42 PM 09-02-2014
Quote:
Originally Posted by 3ll3d00d View Post
Does omnimic let you change the sweep length? What does the ir look like in omnimic? Same as REW or different.

You, and Jerry, could also try HolmImpulse if you want another data point. This would help isolate either the app or the mic/signal chain.
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Here is the OM IR.

Yep. The pre hump is there.

OM works completely differently than REW. You cannot change sweep lengths. You get a CD disc with sweeps contained on them for apllication to different measurements.. The sweep length for FR (shorter) is different than the one used for ETC (longer) though.
Attached:
AustinJerry's Avatar AustinJerry 01:52 PM 09-02-2014
Quote:
Originally Posted by AustinJerry View Post
I guess I'll start over now.
I was trying to be humorous, guys. I'm not going to lose any sleep over this anomaly.
jim19611961's Avatar jim19611961 01:56 PM 09-02-2014
Quote:
Originally Posted by AustinJerry View Post
I was trying to be humorous, guys. I'm not going to lose any sleep over this anomaly.
If we see you posting at 3:00am, then we will know things are worse than your admitting
LastButNotLeast's Avatar LastButNotLeast 02:16 PM 09-02-2014
Make sure Windows isn't adding any of its own processing:


jim19611961's Avatar jim19611961 02:23 PM 09-02-2014
Quote:
Originally Posted by LastButNotLeast View Post
Make sure Windows isn't adding any of its own processing:

Checked that also (had already been disabled).
Kal Rubinson's Avatar Kal Rubinson 04:22 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
Additionally, PE said there was "extra stuff" in the OM version. They added it may not work right with anything other than OM. Made my day
I've used it with REW and with DiracLive.
jim19611961's Avatar jim19611961 04:29 PM 09-02-2014
Quote:
Originally Posted by Kal Rubinson View Post
I've used it with REW and with DiracLive.
I have been using it with REW as well. But if you have been following this recent discussion, and you run the tests prescribed, you may find that there are issues. Especially someone such as your self, who uses a USB mic with REW, could be helpful in determining the cause, whether your suffer from the issue or not.
Kal Rubinson's Avatar Kal Rubinson 04:47 PM 09-02-2014
Quote:
Originally Posted by jim19611961 View Post
I have been using it with REW as well. But if you have been following this recent discussion, and you run the tests prescribed, you may find that there are issues. Especially someone such as your self, who uses a USB mic with REW, could be helpful in determining the cause, whether your suffer from the issue or not.
I have not been "following" this thread with any regularity. Can you explain or link me to it?
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